1. Field of the Invention
The present invention relates to a fuel cell, and more particularly to a fuel cell module of a fuel cell.
2. Description of Related Art
Fuel cells, having advantages of high efficiency, low noise, and no pollution, are an energy technology following the trend of the age. Fuel cells can be divided into many types, in which proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are the common ones. For example, a fuel cell module of a direct methanol fuel cell includes a proton exchange membrane, a cathode and an anode respectively disposed on two sides of the proton exchange membrane.
In view of the above, a fuel (aqueous methanol solution) introduced into the anode generates a chemical reaction by the use of a catalyst and produces hydrogen ions and electrons. The hydrogen ions pass through a proton exchange membrane and goes to the cathode, and the electrons goes to the cathode through a circuit. Then, the hydrogen ions and electrons generate a chemical reaction with oxygen gas of the cathode by the use of the catalyst and produce water. At this time, the fuel cell forms a usable current due to the flow of the electrons.
FIG. 1 is a top view showing a conventional fuel cell module. FIG. 2 is a cross-sectional view taken along line I-I′ in FIG. 1. Referring to FIGS. 1 and 2, a conventional fuel cell module 100 includes two membrane electrode assemblies (MEAs) 110, two printed circuit boards (PCBs) 120, two anode collectors 130, an anode flow channel plate 140, and two cathode collectors 150. Each of the MEAs 110 includes a proton exchange membrane 112, an anode 114, and a cathode 116, in which the anode 114 and the cathode 116 are respectively disposed on two sides of the proton exchange membrane 112. Each of the anode collectors 130 is disposed on one of the anodes 114, the anode flow channel plate 140 is disposed on the anode collector 130, and the anode collector 130 is disposed between the anode 114 and the anode flow channel plate 140. Each of the PCBs 120 presses on an edge of the cathode 116, and each of the PCBs 120 has an opening 122. Each of the cathode collectors 150 is disposed on one of the cathodes 116 and inside the opening 122 of each of the PCBs 120 correspondingly.
During the operation of the fuel cell module 100, the proton exchange membrane 112 of each of the MEAs 110 hydrates with water, so that the hydrogen ions produced by the anode 114 are delivered to the cathode 116. However, the proton exchange membrane 112 swells after absorbing water, thus leading to the expansion of the entire MEAs 110. Since the edge of the MEAs 110 is pressed by the PCBs 120, the central portion of the MEAs 110 protrudes outward, and the cathode collectors 150 also protrude accordingly.
FIG. 3 is a schematic view showing the fuel cell module having the MEA in FIG. 2 after hydration. Referring to FIG. 3, the fuel cell module 100 further includes two cathode flow channel plates 160 disposed beside each of the cathode collectors 150, so as to form a flow channel 170 between each of the cathode flow channel plates 160 and each of the MEA 110 correspondingly. However, since the central portion of the MEAs 110 and the cathode collectors 150 protrude outward, the height of the flow channel 170 is non-uniform. Thus, the height D1 of the central portion of the flow channel 170 is lower than the heights of two sides of the flow channel 170, so the flow resistance of the central portion of the flow channel 170 is greater than the flow resistances of two sides of the flow channel 170. Therefore, most of the gas flow flows through the two sides of the flow channel 170, such that the gas flow at the central portion of the flow channel 170 is too low. As a result, the reaction efficiency of the fuel cell module 100 is reduced.